1. Field of the Invention
The present invention relates to a wireless base station, a communication system, a belonging information management method, and a storage medium for storing a program used for, for example, wireless meshed network, communication between wireless base stations to which a wireless communication terminal belongs, and for performing transmission/receiving of management information of the terminal belonged.
2. Description of the Related Art
Wireless meshed network system is a network in which a plurality of base stations are connected by wireless communication, and a terminal belongs to any one of base stations at certain time. Belonging information is necessary to grasp to which base station belongs which terminal, while belonging information of all terminals belonging to a certain base station are referred to as LAB (Local Association Base). Further, belonging information of all base stations, that is, universal set of LAB, is referred to as GAB (Global Association Base).
In the wireless meshed network, communication between terminals is realized by that each base station has GAB. Further, notification of a change in belonging information and synchronization of GAB (belonging information management table) for managing belonging information are realized by notifying LAB routinely by LABA (Local Association Base Advertisement) message between wireless base stations.
In addition, if all base stations notify large-sized LAB routinely each other, wireless band is consumed greatly resulting in poor efficiency, and therefore, checksum diffusion mode, in which only checksum of LAB is notified by LABCA (Local Association Base Checksum Advertisement) message, is provided (see, for example, “Ad-hoc Meshed Network-Towards Realization of Ubiquitous Network Society”, Corona Publishing, Sep. 20, 2007, p. 171˜174, Kenichi Mase and other 1).
In recent years, wireless communication terminals, which realize a phone call through packet network using VoIP (Voice over IP), have been promulgating. For these terminals, realization of movements between base stations while maintaining communication is important for realization of smooth conversation while maintaining mobility of wireless terminals.
Further, as related technology of the present invention, such one is mentioned that in order to correspond to out-of-synchronization, parent station of a terminal parent station of which is unknown is searched using station information request frame and station information response frame (see, for example, Japanese Patent Application Laid-Open No, 2006-311549).
Further, as related technology of the present invention, such one is mentioned that buffer state synchronization signal including sequence number of a buffer and discard request message is transmitted by a base station to another base station to cause also destination base station to discard data as many as a designated number so as to synchronize data storage state in the buffer (see, for example, Japanese Patent Application Laid-Open No. 2003-78937).
Next, description will be given of the problems of the above related arts. At first, according to the method shown in “Ad-hoc Meshed Network-Towards Realization of Ubiquitous Network Society”, Corona Publishing co., ltd., Sep. 20, 2007, p. 171-174, Kenichi Mase and other 1, LAB is notified every predetermined constant frequency, and therefore, there is a possibility that it takes a long time before a change in LAB due to movement of wireless terminal is reflected to GAB of other base station.
In other words, synchronization of a belonging information management table for managing belonging information does not take place before transmission frequency comes after update, and there is a possibility that communication disconnection time is generated in terminals that moved during this period of time.
Further, if transmission frequency of LAB message is shortened to shorten the communication disconnection time, unnecessary traffics needed for synchronization of the belonging information management table increase, and there is a possibility that a band is compressed unnecessarily.
Further, for the checksum diffusion mode, there is no way but wait for next notification frequency after a difference of GAB is detected and before a latest LAB is obtained, and thus time as much as one frequency is further necessary before synchronization is obtained.
Further, if communication disconnection is caused due to influences of wireless interference or the like and a plurality of differences are caused with regard to GAB of other base station due to that update of GAB is not possible for a certain period, there is no way but wait for LABA messages from a plurality of base stations. For this reason, there is a possibility further time is needed for synchronization of GAB.
Further, when all base stations perform flooding of LAB with a constant frequency, number of messages increases if seen from whole network, and there is a problem that network band is compressed.
Further, according to Japanese Patent Application Laid-Open No. 2006-311549, information of belonging terminals are managed such that wireless LAN module performs request for information about mobile station by broadcast method and its response is obtained by unicast method, unnecessary traffic for synchronization increases by broadcast at every request, and there is a possibility that the band is compressed unnecessarily.
Further, even if update information about the mobile station is received, newness of the update information can not be confirmed.
That is, the consideration given does not cover an application even to such an environment where there is a possibility for receiving update notification information from a plurality of wireless base stations such as base stations in the wireless meshed network.
Further, according to Japanese Patent Application Laid-Open No. 2003-78937, storage state of user data in a buffer is synchronized with regard to other base station by buffer state synchronization signal, and the consideration given does not cover even synchronization of the belonging information management table in an environment where there is a possibility for receiving update notification information from a plurality of wireless base stations such as base stations in the wireless meshed network.
The present invention has been developed in view of the situations and an exemplary object of the present invention is to provide a wireless base station, a communication system, a belonging information management method and a storage medium for storing a program which do not need unnecessarily large traffic generation for synchronization of a belonging information management table even for a case where a plurality of unsynchronized differences are caused and capable of synchronizing the belonging information management table promptly and reliably even in an environment where there is a possibility that update notification information is received from a plurality of wireless base stations.